Actuator and actuation method

1. An actuator, comprising:

a cavity containing a working medium that reversibly expands as it undergoes a phase change from a solid to a liquid state;

a diaphragm disposed adjacent the cavity such that expansion and contraction of the expandable working medium causes the diaphragm to deflect;

a semiconductor element disposed in the cavity, wherein the semiconductor element is operable in a first mode to heat the working medium to cause it to undergo the phase change into the liquid state, and is operable in a second mode to measure the temperature at the semiconductor element, wherein in the first mode, a first constant current is applied across the semiconductor element to heat the working medium, and in the second mode, a second constant current lower than the first constant current is applied across the semiconductor element, a voltage drop across the semiconductor element is measured, and the voltage drop is used to infer the temperature at the semiconductor element.

2. An actuator according to claim 1 , wherein the semiconductor element is a diode.

3. An actuator according to claim 1 , comprising control circuitry for setting a pulse start time and a pulse duration for applying an electric current to the semiconductor element, at least one of the pulse start time and pulse duration being set in dependence on the temperature measured by the semiconductor element.

4. An actuator according to claim 3 , wherein the deflection of the diaphragm is used to pump a therapeutic product to a patient.

5. An actuator according to claim 4 , wherein in a basal delivery mode, the control circuitry is operable to set the pulse duration in dependence on the temperature measured by the semiconductor element just before the pulse is due to be started.

6. An actuator according to claim 4 , wherein in a bolus delivery mode, the control circuitry is operable to trigger the start of a new pulse when the temperature measured by the semiconductor element has dropped to a predetermined temperature following the end of the previous pulse.

7. An actuator according to claim 6 , wherein the pulse duration of each new pulse is set in dependence on the predetermined temperature.

8. An actuator according to claim 5 , wherein in the basal delivery mode, the control circuitry is operable to control the rate of delivery of the therapeutic product by setting the frequency with which pulses of electric current are applied to the semiconductor element.

9. An actuator according to claim 5 , wherein in the basal delivery mode, the control circuitry is operable to monitor an amount of therapeutic product delivered over the previous n pulses, wherein n is an integer value greater than zero, and to modify a pulse parameter in relation to the next one or more pulses in dependence on a difference between an intended delivery quantity and an actual delivery quantity over those n pulses.

10. An actuator according to claim 9 , wherein the pulse parameter is the duration of the next one or more pulses.

11. An actuator according to claim 9 , wherein the pulse parameter is an interval between successive pulses.

12. An actuator according to claim 11 , wherein if the actual delivery quantity is less than the intended delivery quantity then the duration of the next pulse is increased by an amount which is dependent on the magnitude of the difference, and if the actual delivery quantity is more than the intended delivery quantity then the duration of the next pulse is decreased by an amount which is dependent on the magnitude of the difference.

13. An actuator according to claim 6 , wherein in the bolus delivery mode, the control circuitry is operable to deliver a predetermined bolus dose by calculating a first schedule of successive pulses required to deliver a first portion of the predetermined bolus dose, applying the calculated first schedule of successive pulses, determining an amount of therapeutic product delivered over the first schedule of successive pulses, calculating a second schedule of successive pulses required to deliver a next portion of the predetermined bolus dose in dependence on either a difference between an intended delivery quantity for the first portion and an actual delivery quantity delivered over the first schedule, or in dependence on an amount of therapeutic product still to be delivered, and applying the calculated second schedule of successive pulses.

14. An actuator according to claim 13 , wherein the control circuitry is further operable to determining an amount of therapeutic product delivered over a previous schedule of successive pulses, calculate a further schedule of successive pulses required to deliver a next portion of the predetermined bolus dose in dependence on either a difference between an intended delivery quantity for the previous portion and an actual delivery quantity delivered over the previous schedule, or in dependence on an amount of therapeutic product still to be delivered, and applying the calculated further schedule of successive pulses.

15. An actuator according to claim 13 , wherein the control circuitry is further operable to calculate a final schedule of successive pulses when the amount of therapeutic product remaining to be delivered is less than or equal to a predetermined amount.

16. An actuator according to claim 6 , wherein in the bolus delivery mode, the control circuitry is operable to deliver a predetermined amount of therapeutic product by applying a schedule of successive pulses, wherein the control circuitry is responsive to a determination that the predetermined amount of therapeutic product has been delivered before the schedule of successive pulses has been completed to discontinue the delivery of pulses.

17. An actuator according to claim 16 , wherein the schedule of successive pulses comprises a first set of pulses followed by a second set of pulses, each pulse in the first set of pulses having a longer duration than each pulse in the second set of pulses.

18. A therapeutic product delivery device comprising an actuator according to claim 1 .